Axial and perpendicular angle sensor in single package

ABSTRACT

Embodiments relate to magnetic field angle sensors that utilize axial and perpendicular sensors collectively to infer a rotational angle. In embodiments, a sensor system comprises at least one axial sensor unit and at least one perpendicular sensor unit arranged in a single sensor package or on a single substrate. The axial and perpendicular sensor data both representative of the rotational position can be used to improve output angle accuracy by, e.g., calibrating the sensor system.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 14/174,580filed on Feb. 6, 2014, the contents of which are incorporated byreference in their entirety.

FIELD

The invention relates generally to magnetic field sensors, and moreparticularly to magnetic field sensors comprising both axial andperpendicular angle sensors in a single package.

BACKGROUND

Magnetic field sensors can be used to sense an angle of rotation of ashaft. For example, a magnet can be mounted on the shaft such that itrotates with the shaft, and a magnetic field sensor can be arrangedproximate the magnet in order to sense a magnetic field induced by themagnet as it rotates with the shaft. When the magnetic field sensor ismounted next to or adjacent the shaft, i.e., off of the axis of rotationof the shaft, the sensor is often referred to as an “off-axis” magneticfield angle sensor. Off-axis magnetic field angle sensors often areimplemented when the end of the shaft is unavailable as a location forthe sensor or there simply is not space available on the shaft. An“on-axis” magnetic field sensor is one in which the sensor is mounted ator near the end of the shaft, generally in-line with or on the axis ofrotation. Examples of off-axis and on-axis sensors are perpendicularangle sensors and axial angle sensors.

Axial angle sensors are magnetic field angle sensors that utilize theaxial magnetic field component to infer the rotation angle. The sensorsperform optimally with fields that are linearly varying in twocomponents and must be arranged in an off-axis configuration because theaxial magnetic field component cannot be detected on the axis ofrotation for many types of common magnets such as diametricallymagnetized magnets of rotational shape. An additional feature of axialangle sensors is that the sensors are robust against external magneticdisturbances. Perpendicular angle sensors, on the other hand, performoptimally with homogeneous magnetic fields and utilize radial andazimuthal magnetic field components to infer a rotation angle. Theperpendicular angle sensors can be manufactured for robustness againstassembly tolerances and can be arranged in an on-axis configuration. Inmany applications there is a general preference for magnetic field anglesensors, whether off- or on-axis or axial or perpendicular, to beinexpensive while also being robust with respect to external magneticfields and other disturbances. A drawback of some perpendicular anglesensors, then, is that they are not robust against external magneticfields and other disturbances. While axial sensors are more robust withrespect to these disturbances, axial sensors are more sensitive toassembly tolerance errors. Other drawbacks to conventional approachesinclude the inability to provide a robust sensor that is capable ofdetecting angles over a full 360 degree range. In general, therefore,there are numerous drawbacks associated with conventional magnetic fieldangle sensors.

SUMMARY

Embodiments relate to magnetic field sensors, such as magnetic fieldsensors comprising both axial and perpendicular angle sensors in asingle package.

In an embodiment, a magnetic field sensor system comprises a supportstructure; a first sensor arranged on the support structure relative toan axis of rotation of a magnetic field source and comprising a firstplurality of sensor elements configured to sense magnetic fieldcomponents along a first direction and to derive a first rotation angleunambiguously in a range of at least 90 degrees; and a second sensorarranged on the support structure relative to the axis of rotation andcomprising a second plurality of sensor elements configured to sensemagnetic field components along a second direction different from thefirst direction and to derive a second rotation angle unambiguously in arange of at least 70 degrees, wherein only one of the first direction orthe second direction is perpendicular to the axis of rotation.

In an embodiment, a method comprises providing a sensor systemcomprising a first sensor and a second sensor coupled to a supportstructure; sensing magnetic field components along a first direction bythe first sensor to derive a first rotation angle unambiguously in arange of at least 90 degrees; sensing magnetic field components along asecond direction different from the first direction by the second sensorto derive a second rotation angle unambiguously in a range of at least70 degrees; and calibrating the sensor system using at least one of thefirst rotation angle or the second rotation angle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 depicts a perspective diagram of a magnetic field angle sensoraccording to an embodiment.

FIG. 2 depicts a block diagram of a sensor package according to anembodiment.

FIG. 3 depicts a top view of a sensor package arranged on a substrateaccording to an embodiment.

FIG. 4 depicts a top view of a sensor package arranged on a substrateaccording to an embodiment.

FIG. 5 depicts a top view of a sensor package arranged on a substrateaccording to an embodiment.

FIG. 6 depicts a flow chart diagram of a method according to anembodiment.

FIG. 7A depicts a top sectional view of a sensor system packageaccording to an embodiment.

FIG. 7B depicts a side sectional view of a sensor system packageaccording to an embodiment.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Embodiments relate to magnetic field angle sensor systems that utilizeaxial and perpendicular sensors collectively to infer a rotationalangle. In embodiments, a sensor system comprises at least one axialsensor and at least one perpendicular sensor arranged in a single sensorpackage or on a single substrate. The axial and perpendicular sensordata both representative of the rotational position can be used toimprove output angle accuracy by, e.g., calibrating the sensor system.For example, in one embodiment the perpendicular sensor can provide afirst estimate or approximation of the rotational position, the axialsensor can provide a second estimate or approximation of the rotationalposition, and the sensor system or circuitry coupled thereto can combinethe first and second estimates.

The terms “perpendicular angle sensors” and “axial angle sensors” arereferred to in the article Ausserlechner, “A Theory of Magnetic AngleSensors with Hall Plates and Without Fluxguides,” Progress inElectromagnetics Research B, Vol. 49, 77-106, 2013, which isincorporated herein by reference in its entirety.

Referring to FIG. 1, an example of a sensor system 100 is depicted.Sensor system 100 comprises a magnet 102 mounted or otherwise affixed toa shaft 104 such that magnet 102 rotates with shaft 104. A sensorpackage 105 comprises a substrate 106 and is arranged proximate magnet102 and shaft 104. In various embodiments, substrate 106 can comprise asubstrate, a semiconductor die, a leadframe coupled with one or moresemiconductor dies, a component board, a combination thereof or someother support structure capable of establishing and/or maintaining anaccurate or relative placement of sensors 110 and 111 with respect toeach other and/or at least one other component. For example andsimplicity, the term “substrate” will generally be used hereinthroughout but is not limiting with respect to all embodiments and/orthe scope of the claims. In sensor system 100, sensor package 105 isarranged coaxially with shaft 104, with substrate 106 orientedperpendicularly thereto. A major plane of substrate 106, i.e., thexy-planar surface facing upwardly in the orientation of FIG. 1, isarranged perpendicularly to the rotation axis of shaft 104 asillustrated. In other embodiments, substrate 106 can be arranged withthe xy-planar surface facing downwardly away from magnet 102.

In embodiments, sensor package 105 comprises at least two axial sensors110 and at least two perpendicular sensors 111 arranged on substrate106. When referring to sensor 110, “axial” generally refers to a sensorthat comprises two or more magnetic sensor elements that are responsiveto axial magnetic field components and derives the rotational positionof magnet 102 by combining the output signals of the two or moremagnetic sensor elements. In addition, when referring to sensor 111,“perpendicular” generally refers to a sensor that comprises two or moremagnetic sensor elements that are responsive to magnetic fieldcomponents perpendicular to the axis of rotation. While one or the othersensor 110 or 111 may be identified as axial or perpendicular inexamples given herein, these designations can be reversed with oneanother or have some other configuration in other embodiments.Additionally, the depiction of sensor system 100 in FIG. 1 is merely asimplified diagram of basic components, which are not to scale and theplacement and relative arrangement of which can and will vary in otherembodiments. The relative position of substrate 106 and magnet 102 canvary in embodiments, as can the relative arrangement and orientations ofaxial sensor 110 and perpendicular sensor 111, with FIG. 1 beingexemplary of but one embodiment. For example, in other embodiments,sensors 110 and 111 of sensor package 105 may be arranged separately ontwo substrates, proximate (e.g., concentric, adjacent or in some otherarrangement) one another on a single die, in a die-on-die configuration,or arranged adjacently on both sides of a lead frame. Moreover, FIG. 1is not to scale and is a simplified conceptual depiction to illustratebasic components and features of an embodiment of sensor system 100.Other example embodiments will be discussed elsewhere herein.

Magnet 102 has a diametric magnetization in the direction indicated inFIG. 1, i.e., the y-direction, and induces a magnetic field that isperpendicular to the rotation axis of shaft 104 and magnet 102. In otherembodiments, magnet 102 can have an additional or sole axialmagnetization or comprise some other type of magnet. Axial sensor 110 issensitive to magnetic field components which are perpendicular to thexy-planar surface of substrate 106 (i.e., axial with respect to therotation axis). Perpendicular sensor 111 is sensitive to magnetic fieldcomponents which are parallel to the xy-planar surface of substrate 106(i.e., perpendicular with respect to the rotation axis).

In embodiments, axial sensor 110 and perpendicular sensor 111 each cancomprise at least two sensor elements configured to sense thecorresponding magnetic field components to which each sensor isconfigured to detect. For example, axial sensor 110 can comprise atleast two sensor elements, such as a Hall-effect sensor element (e.g.,Hall plate), MAGFET and/or other type(s) of magnetic field sensorelements or combinations thereof configured and/or arranged to detect atleast one magnetic field component. Similarly, perpendicular sensor 111can comprise at least two magnetic field sensor element, such as amagneto-resistive (MR) sensor element (e.g., AMR, GMR, TMR and others),giant magneto-impedance (GMI) sensor element, Hall-effect sensorelements (e.g., vertical Hall and others) and other magnetic fieldsensor elements and combinations thereof. As previously discussed,although the relative arrangement of sensors 110 and 111 can vary inembodiments, it can be advantageous in embodiment to establish accurateplacement of sensor 110 with respect to sensor 111 such that sensorpackage 105 and/or substrate 106, and sensors 110, 111, havecorresponding mounting tolerances. Thus, various techniques can be usedsuch as manufacturing both sensors 110 and 111 in the same manufacturingsequence, e.g., a microelectronic fabrication front-end line whichdefines the relative position of all elements by lithographic steps orother similar techniques to establish accuracies up to sub-micrometers(e.g, better than about 20 μm).

Referring to FIG. 2, a sensor substrate 106 is shown according to anembodiment. Substrate 106 can be arranged on or in a sensor package(e.g., 105 in FIG. 1) in embodiments. In embodiments, axial sensor 110can comprise a plurality of sensor elements 206. The plurality of sensorelements 206 can comprise horizontal Hall (HHall), MAGFET or othersuitable magnetic field sensor elements. In the embodiment of FIG. 2,axial sensor 110 comprises eight sensor elements 206 arrangedsymmetrically and equidistantly angularly spaced along a circular curveon substrate 106. The circular curve can be centered on, e.g., aprojection of the axis of rotation of shaft 104 and/or magnet 102 ontosubstrate 106 in an embodiment. In FIG. 2, adjacent ones of theplurality of sensor elements 206 are spaced apart from one another byabout 45 degrees along the circular curve. In embodiments, sensorelements 206 are sensitive to an axial magnetic field component Bz,whereby the Bz field component is perpendicular to the xy-planar surfaceof substrate 106. Axial sensor 110 can be configured in embodiments tooutput an angular range of 360 degrees to provide continuous andunambiguous detection of the axial magnetic field components, ascompared with some conventional sensor systems having only 180 degreesof unambiguous output range.

In embodiments, perpendicular sensor 111 can comprise at least twosensor elements 208, such as four sensor elements 208 a-d in theembodiment of FIG. 2, arranged proximate a center of a projection of therotation axis of shaft 104 and/or magnet 102 on substrate 106. Sensorelements 208 can comprise magneto-resistive or Hall sensor elements suchas TMR, GMR, or still other suitable sensor elements in variousembodiments. In embodiments, sensor elements 208 a-d of perpendicularsensor 111 can be coupled to form first and second evaluation circuits202, 204. In example embodiments, first and second evaluation circuits202, 204 can be configured to form two half-bridge circuits asillustrated in FIG. 2 or any other circuits specific to an applicationor sensor requirement. Each evaluation circuit 202, 204 can beconfigured to measure perpendicular magnetic field components (e.g., Bx,By) and calculate (or provide for calculation by an external circuit ordevice) a corresponding cosine and sine function of the magnetic fieldcomponent angle. Alternatively, evaluation circuit 202, 204 can beconfigured to measure cosine, sine, or square of cosine or sine in thecase of AMRs, of an angle between a projection of the magnetic fieldonto the xy-plane and a reference direction. In such a configuration,for example, the reference direction can be denoted by an arrow symbolas depicted in FIG. 2, and evaluation circuit 202 can provide an outputsignal that is proportional to the cosine of the angle between theprojection of the magnetic field onto the xy-plane and a positivex-direction. In other embodiments, sensor elements 208 can be sensitiveto other field components depending upon the particular arrangement ofsubstrate 106, sensor elements 208, shaft 104 and/or magnet 102. Firstevaluation circuit 202 can comprise sensor elements 208 a, 208 barranged symmetrically in a 180-degree orientation from one another(i.e., generally in-line with one another in at least one embodiment),whereby sensor element 208 a is electrically coupled to sensor element208 b to form evaluation circuit 202. Each sensor element 208 a, 208 bis configured to respond to the angle between the reference direction(i.e., positive or negative x-direction) and the in-plane projection(i.e., xy-projection) of the applied magnetic field. Second evaluationcircuit 204 can comprise sensor elements 208 c, 208 d arrangedsymmetrically in 180 degree orientation from one another to form anelectrical series connection. Each sensor element 208 c, 208 d ofevaluation circuit 204 can be configured to respond to the angle betweenthe reference direction (i.e., positive or negative y-direction) and thein-plane projection (i.e., xy-projection) of the applied magnetic field.The arrangement of sensor elements 208 a-d as described herein is merelyexemplary and can vary in other embodiments in which, for example, moreor fewer sensor elements can be provided.

In embodiments, evaluation circuits 202, 204 can be configured togenerate an output signal Outx and/or Outy related to an angularposition of magnet 102, wherein those signals are induced by thepresence of a magnetic field associated with the radial and azimuthalfield components. For example, the presence of a magnetic field cancause a resistance change in sensor elements 208 a-d, such that theresistance of sensor elements 208 a and 208 b increases as theresistance of sensor elements 208 c and 208 d decreases. As such, thechange in resistance can be characterized by signals provided at Outxand Outy. The size and magnitude of each sensor element 208 a-d can varyin embodiments where, for example, individual resistor sizes can rangefrom several about hundred Ohms to relatively large sizes of about 50 kOhms or greater. Similarly, as previously discussed, perpendicularsensor 111 can comprise various magneto-resistive sensor elements 208a-d, whereby the use of sensor elements such as TMR, for example, cangenerate larger output signals Outx, Outy that allow for raw (i.e.,non-scaled) data to be processed by an external processing unit (e.g.,computer, controller, processor or other circuitry in embodiments). Inaddition, the use of TMR sensor elements in embodiments can beadvantageous in that: i) no additional chip space is required becausethe sensor elements can be sputtered above substrate 106 which comprisesboth axial sensor 110 and signal conditioning circuitry, ii) the use ofbias circuitry can be avoided because the sensor elements can bearranged in a full or half bridge circuit that is supplied by a voltagesource, iii) signal conditioning is not required because the outputvoltages are strong (e.g., >100 mV) such that the voltages can bemeasured directly by any voltmeter connected to the sensor, iv) offseterrors are negligible because of the high magnetic sensitivity and othererrors (e.g., synchronicity between orthogonal bridges and orthogonalityerrors or temperature dependence of various parameters which arecancelled out in the output signal in first order) are also negligible,and v) current consumption can be reduced below 100 μA at 2V supply.

In embodiments, and in operation, evaluation circuits 202, 204 can beconfigured to selectively power on and off perpendicular sensor 111 toreduce the amount of power consumed by sensor system 100. For example,during installation or calibration, system 100 can use sensor 111 toidentify the magnitude of assembly tolerances, whereas during normaloperation axial sensor 110 can be used alone, in one embodiment. Inembodiments, evaluation circuits 202, 204 can be electrically coupled toa supply source via a positive potential (Vsup) and reference potential(Gnd) that provide power to perpendicular sensor 111, whereby thereference potential (Gnd) can be collectively used by both axial sensor110 and perpendicular sensor 111 such that sensor 111 has a dedicatedpositive potential (Vsup). In such a configuration, perpendicular sensor111 can be selectively powered off either by disconnecting the positivepotential (Vsup) or by connecting the positive potential (Vsup) to thereference potential (Gnd) while axial sensor 110 remains powered. Inother embodiments, for example, sensor elements 208 a-d can beconfigured with relatively high resistances (e.g., greater than 50 kOhms in embodiments) to reduce the need for additional circuitry toremove power from perpendicular sensor 111, whereby the high resistancescan result in a simultaneous decrease in the amount of current consumedby sensor system 100. Although perpendicular sensor 111 can experienceincreased noise as a result of the use of relatively high resistances,this can be addressed by having longer measurement times (i.e., longerintegration times) and/or a larger number of sampled data because therotational speed can be reduced during calibration. These exampleembodiments are for illustration purposes only and are in no waylimiting to other or all embodiments.

Referring to FIGS. 3 and 4, another embodiment is depicted. In FIGS. 3and 4, axial sensor 110 comprises a plurality of sensor elements 310,410 and perpendicular sensor 111 comprises a plurality of, such as atleast three, sensor elements 311, 411 arranged on substrate 106. Similarto sensor elements 206 of the embodiment of FIG. 2, sensor elements 310and 410 can be arranged symmetrically and equidistantly angularly spacedalong a closed curve that can be circular as depicted in FIGS. 3 and 4,or another closed curve such as a square or some other shape inembodiments, an open curve, or some other suitable arrangement, and cancomprise horizontal Hall (HHall), MAGFET or other suitable magneticfield sensor elements. In embodiments, sensor elements 311 a-d cancomprise vertical Hall sensor elements in which the sensor elements areresponsive to magnetic field components Bx and By that are parallel tothe xy-planar surface of substrate 106 (i.e., perpendicular with respectto the rotation axis). As depicted in FIG. 3, sensor elements 311 a-dcan be arranged proximate a center of a projection of the rotation axisof shaft 104 and/or magnet 102 on substrate 106 and can be oriented in90-degree rotation from adjacent ones of sensor elements 311 and can beequidistantly angularly spaced from one another. Sensor elements 311 a-dcan have relatively small dimensions in embodiments and be centrallyarranged with respect to the projection of the rotation axis to increasethe precision of the measured magnetic field angles.

An additional technique to increase the accuracy of the measured anglescan be to reduce an offset voltage (i.e., an output voltage at the sensecontacts of a sensor device in the absence of a magnetic field) atsensor elements 311 a-d. To reduce the offset voltage, sensor elements311 a-d can be configured as dynamic offset compensation circuits (e.g.,spinning current, spinning voltage or other suitable operationalschemes), whereby the circuit can be configured to continuously corrector compensate the measured output voltage. For example, the spinningcurrent technique can utilize a Hall device with a number ofsymmetrically arranged contacts (e.g., four or eight contacts) to inducea spinning current (i.e., current induced by electrical commutationwhich is applied to different contacts in different phases, wheredifferent contacts also can be used as reference and signal contacts inthose phases). In such a configuration, offset errors (e.g., voltageerrors) can be reduced by averaging a measured output signal of sensorelements 311 a-d, whereby the output signals can be relatively small andbe processed on- or off-chip (i.e., analyzing the output signal by anexternal processing unit or circuit) to provide an estimated anglemeasurement. In other embodiments, each sensor element 311 a-dcomprising vertical Hall effect devices or other magnetic sensorelements can be configured to share circuit components such asamplifiers, digital to analog converters, biasing circuits, etc., whichcan also result in a reduction of assembly costs. Such a scheme can beused in other embodiments and/or applied to other sensor elements invarious embodiments.

In still other embodiments as depicted in FIG. 4, sensor elements 411a-d can comprise AMR sensor elements, whereby a reference directionassociated with the magnetic field component is determined by thedirection of current flow irrespective of its polarity. Sensor elements411 a-d can be coupled to form first and second evaluation circuits 402and 404 similar to the embodiment discussed with reference to FIG. 2,such that evaluation circuits 402, 404 can be configured to form twohalf-bridges A and B (i.e., A1, A2 . . . An or B1, B2 . . . Bn) as shownin FIG. 4 according to a single reference direction. In embodiments, thesensor element subparts can be arranged in an alternating arrangement(i.e., A1, B1, A2, B2 . . . AnBn) along a circular curve or in a commoncentroid arrangement (i.e, A1, B1 . . . B(n-1), A(n-1), An, Bn). Thealternating or centroid arrangement of sensor elements 411 on substrate106 can lead to a reduction in angle errors because of the finite sizeand dimensions of sensor elements 411. The angle readings generated byperpendicular sensor 111 can be limited to a continuous 180 degreeangular range in embodiments. The limited 180-degree angular range ofperpendicular sensor 111 can be used to calibrate axial sensor 110within a range of 360 degrees. For example, the angular range 0° to 180°can be measured by both sensors, yet perpendicular sensor 111 comprisingAMR sensor elements can map the range 180° to 360° onto 0° to 180° whileaxial sensor 110 measures an angular range of 0° to 360° uniquely.

As a result of assembly tolerances, both sensors 110 and 111 may showslightly different values. During calibration, disturbance fields aredesired to be avoided, and the angle measurement provided by sensor 111can be used because it is more accurate in spite of assembly tolerancesat least in the angular range 0° to 180°. In the range of 180° to 360°,sensor 111, for example, outputs 3° while the axial sensor 110 outputs181°. The 3° output by sensor 111 in fact corresponds to 183°, whichsensor 111 maps to 3°, whereas axial sensor 110 outputs 181° instead ofthe accurate 183° due to assembly tolerances. As such, angle errorsassociated with axial sensor 110 can be identified by use of sensor 111comprising AMR sensor elements 411 although AMR sensor elements are notunique in the angular range 0 to 360°. Therefore, to improve angleaccuracy, system 100 can be configured to correct the measured output ofsensor 110 to correspond to the measured value of sensor 111 (e.g., ifaxial sensor 110 outputs 181° it has to add 2° to obtain the accuratevalue 183°). During operation in the field (i.e., normal operation),disturbance fields may exist such that system 100 can rely solely on theoutputs from axial sensor 110 because it is robust against disturbances.If perpendicular sensor 111, for example, outputs 5° instead of 3° at183°, system 100 will only use readings from axial sensor 110 and add 2°to the reading if the reading is around 183°. Although perpendicularsensor 111 is not robust against disturbance magnetic fields as axialsensor 110, sensor 111 can still be operated in the field in order tosupply a second rotation angle, which can be used to verify (e.g., atleast with an accuracy of about +/−5°) if the axial angle sensor isworking correctly. Thus, circuitry such as a microprocessor can beconfigured to measure both angles, whereby the output of axial sensor110 is used as an estimation and the output of perpendicular sensor 111is used as a redundant information source to increase the reliability ofsystem 100 (i.e., to increase functional safety features).

Referring to FIG. 5, and regardless of the particular configuration orembodiment of sensor package 105, substrate 106, axial sensor 110 and/orperpendicular sensor 111, sensor system 100 can further comprise acontrol unit 520 coupled to an output of axial sensor 110 andperpendicular sensor 111 and configured to determine an estimation of arotation angle. In embodiments, control unit 520 can comprise or becoupled to memory circuitry 522. Control unit 520 and/or memorycircuitry 522 can be external but coupled to sensor 105, and/or memorycircuitry 522 can be external to control unit 520, with the depiction inFIG. 5 being exemplary of but one embodiment. In embodiments, memorycircuitry 522 can be utilized to store an offset value or other datacomputed by control unit 520. As previously described, sensors 110 and111 can be configured to sense their respective magnetic fieldcomponents associated with a rotational position of magnet 102. Inembodiments, control unit 520 can be configured to process outputsignals Sa and Sb by, e.g., computing the sine and cosine functions ofSa and Sb, to determine a rotational angle, and calculating a differencein angles derived from S_(a1), S_(a2) and S_(b1), S_(b2).

In embodiments, the angle difference computed by control unit 520 can beused to identify outliers (i.e., defective sensors or sensor elements)and/or to determine a difference in angle estimations from sensor 110and sensor 111 to improve the accuracy of sensor system 100 anglemeasurements. For example, during calibration system 100 compares theestimated angles of both sensor 110 and 111 to compute the angledifference. As such, the angle difference can be used to determine adegree of variation of the measured angles from the actual angles due toassembly tolerances, whereby a large (e.g., greater than 5 degrees, orsome other suitable threshold in other embodiments) angle difference canindicate a large angle error. Additionally, during other operatingconditions the angle difference can be used as an offset to correctangle errors associated with axial sensor 110 by summing the value witheach output of sensor 110. During such operating conditions, axialsensor 110 can be used exclusively because it is robust againstdisturbances as discussed with reference to FIG. 4. In other words, theuse and combination of two different sensors 110, 111 can take advantageof strengths or advantages of one that compensate for or remedyweaknesses or disadvantages of the other. Thus, individual values and/orall values associated with a defective or underperforming sensor elementcan be identified and/or removed from consideration in calculations andother determinations. Moreover, a more fundamental recognition ofcircumstances in which one or the other of the sensors 110 or 111 isstronger or weaker can be addressed by operating the sensor in a mannerthat takes advantage of the strength, minimizes the weakness and/orcompensates one for the other by the two sensors 110, 111.

For example, and referring to FIG. 6, a flow chart according to anembodiment is depicted. In embodiments, a method 600 can be used toidentify angle errors generated by axial sensor 110 and perpendicularsensor 111. At 602, sensor system 100 is provided, whereby eachcomponent can be manufactured utilizing CMOS technology or othermanufacturing techniques. In addition, at 602, system 100 is installedand assembled (i.e., sensor package 105 is mounted proximate magnet 102and magnet 102 is attached to shaft 104) to identify tolerances andwhether system 100 can and/or should compensate for the tolerances. At604, and in operation of sensor system 100, a magnetic field can beinduced by rotation of magnet 102, whereby techniques such astemporarily utilizing magnetic shields and/or temporarily inhibiting theoperation of motors can be used to reduce the effects of magneticdisturbance fields. For example, high permeability materials (i.e.,materials with high magnetization) such as alloys or other suitablematerials can be used to create an external barrier or shield aroundmagnet 102 to attract and re-direct magnetic fields through the materialto prevent magnetic fields from causing unintended interference.Similarly, temporarily reducing or removing power supplied to a motorcan reduce the effects of electromagnetic interference caused by use ofthe motors. At 606, the corresponding readings are obtained by measuringoutput signals Sa and Sb. The angle difference between Sa and Sb iscomputed at 608 and can be used to identify and discard outliers (i.e.,defective sensors) at 608. For example, the computed angle differencecan be evaluated to determine the magnitude of angle errors resultingfrom assembly or other tolerances, or other sources. These angledifferences can be computed for a single rotation angle, for someapplication relevant rotation angles, or for many rotation angles withinthe full range of angle occurring during operation. If the angle errorsare outside of a predefined acceptable range, then at 610 defectivesensor systems or parts of it can be discarded.

As discussed with reference to FIG. 2, system 100 can use perpendicularsensor 111 comprising, e.g., TMR sensors elements 208 a-d to identifyangle errors in some embodiments. Sensor elements 208 a-d can beconfigured to form one or more evaluation circuits 202, 204 (i.e.,bridge circuits), whereby sensor elements 208 a-d provide large outputsignals (Sb) that can be measured without signal conditioning byexternal circuitry (e.g., a microprocessor or voltmeter). Thus, the useof TMR sensor elements can be advantageous because system costs arereduced without compromising angle accuracy.

In some embodiments, the computed difference from 608 can be used as anoffset value that is stored in memory 522 at 612. In embodiments,operations 612-618 can be carried out after, concurrent with, insteadof, or in only some periods of operation, with the depiction of method600 in FIG. 6 merely illustrating various operations that can be carriedout in different ways in different embodiments. In one embodiment, oncethe value is stored at 612, a flag can be set at 614, such as apredetermined bit of a register within control unit 520, to notifysystem 100 to switch off a supply signal to perpendicular sensor 111 at616. As previously discussed, perpendicular sensor 111 can be switchedoff by removal of the supply source or by connecting the supplypotential (Vsup) to the reference potential (Gnd) (refer, e.g., to FIG.2). The rotational angle of magnet 102 can then be exclusivelydetermined by axial sensor 110, which can be configured to provide acontinuous and unambiguous angular range of 360 degrees in embodiments.At 618, control unit 520 can sum each output signal Sa of axial sensor110 with the computed offset value to reduce angle errors and to improvethe accuracy of the angle readings measured by axial sensor 110.

For example, as previously discussed, AMR sensor elements can be limitedto a 180-degree angular range. The angular position can be representedby psi, where psi is the angle between a current flowline and themagnetization of a soft magnetic layer of the AMR sensor element. Assuch, utilizing the offset value calculated at 608 in combination withthe output of axial sensor 110, the angular position of sensor system100 can be determined in full 360-degree range (i.e., psi and psi+180).In embodiments, for example, control unit 520 can be configured toevaluate the output of sensors 110 and 111, whereby the output of axialsensor 110 can be used individually to determine angular readingsgreater than 180 degrees (i.e., psi+180). In such regions, the angularreading of axial sensor 110 can be used to estimate a correspondingangular reading of perpendicular sensor 111, whereby the measureddifferences between the angular readings are generally small (e.g., lessthan 5 degrees).

While embodiments discussed herein depict sensors 110 and 111 on asingle substrate, in embodiments sensors 110 and 111 can be arranged onseparate substrates in the same package or in different packages. Forexample, in FIG. 7A, sensor 110 is arranged on a first substrate 702 andsensor 111 is arranged on a second substrate 704 horizontally adjacentthe first substrate, within sensor system package 700. In otherembodiments, substrates 702 and 704 can be closer to and touching oneanother, or can be further spaced apart, differently sized, etc.Substrates 702 and 704 also can be arranged vertically adjacent oneanother, as depicted in FIG. 7B. In other embodiments, the relativepositions of substrates 702 and 704 in either FIG. 7A or 7B can bereversed, and/or in FIG. 7B a die-on-die configuration can beimplemented in which one substrate (or die) is mounted on the other. Inyet another embodiment, a first substrate or die 702 can be arranged ona first side of a leadframe, and a second substrate or die 704 can bearranged on a second side of the leadframe. Still other configurationscan be implemented in other embodiments, and both sensors 110 and 111generally are arranged in the same package but need not be in everyembodiments or configuration.

Embodiments thereby provide systems and methods can detect angle errors,such as those related to assembly errors and tolerances. At least oneapplication of embodiments of the systems and methods discussed can bein end-of-line manufacturing testing and calibration, such as todetermine whether any errors related to assembly tolerances might bepresent in any particular sensor or sensor system. For example, thesensor system can be assembled and mounted proximate a magnetic fieldsource, such as a magnet configured to rotate on an axis of rotation.The magnetic field source can be rotated, and first and second (e.g.,axial and perpendicular) sensor data can be obtained. A differencebetween the axial sensor data and the perpendicular sensor data can bedetermined. Data then can be output (such as the axial and/orperpendicular sensor data, and/or the difference determined), and thedifference data optionally can be stored in the sensor for use duringoperation. In some embodiments, the sensor can be programmed to take thedata into consideration during operation. Periodic implementation duringoperation after end-of-line testing and calibration can be useful todetermine any drift over lifetime or other changes that can occur inoperation, but need not be implemented in all cases.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the invention. It should be appreciated,moreover, that the various features of the embodiments that have beendescribed may be combined in various ways to produce numerous additionalembodiments. Moreover, while various materials, dimensions, shapes,configurations and locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention can comprise a combination of different individual featuresselected from different individual embodiments, as understood by personsof ordinary skill in the art. Moreover, elements described with respectto one embodiment can be implemented in other embodiments even when notdescribed in such embodiments unless otherwise noted. Although adependent claim may refer in the claims to a specific combination withone or more other claims, other embodiments can also include acombination of the dependent claim with the subject matter of each otherdependent claim or a combination of one or more features with otherdependent or independent claims. Such combinations are proposed hereinunless it is stated that a specific combination is not intended.Furthermore, it is intended also to include features of a claim in anyother independent claim even if this claim is not directly madedependent to the independent claim.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

What is claimed is:
 1. A method comprising: providing a sensor systemcomprising a first sensor and a second sensor coupled to a supportstructure; sensing magnetic field components along a first direction bythe first sensor to derive a first rotation angle unambiguously in arange of at least 90 degrees; sensing magnetic field components along asecond direction different from the first direction by the second sensorto derive a second rotation angle unambiguously in a range of at least70 degrees; and calibrating the sensor system using at least one of thefirst rotation angle or the second rotation angle.
 2. The method ofclaim 1, further comprising determining a difference between the firstrotation angle and the second rotation angle.
 3. The method of claim 2,further comprising storing the difference in a memory of the sensorsystem.
 4. The method of claim 2, further comprising eliminating acontribution of at least one sensor element of the first sensor or thesecond sensor based on the difference.
 5. The method of claim 1, furthercomprising providing a signal that is unique over 360 degrees ofrotation and is at least one of: an angle related to the axial magneticfield component, an angle related to the perpendicular magnetic fieldcomponent, or a difference between the axial magnetic field componentand the perpendicular magnetic field component.